Chemical-mechanical polishing (“CMP”) processes are used in the manufacturing of microelectronic devices to form flat surfaces on semiconductor wafers, field emission displays, and many other microelectronic substrates. For example, the manufacture of semiconductor devices generally involves the formation of various process layers, selective removal or patterning of portions of those layers, and deposition of yet additional process layers above the surface of a semiconducting substrate to form a semiconductor wafer. The process layers can include, by way of example, insulation layers, gate oxide layers, conductive layers, layers of metal or glass, and the like. In certain steps of the wafer fabrication process, the uppermost surface of the process layers is desirably planar, i.e., flat, for the deposition of subsequent layers. CMP is used to planarize process layers wherein a deposited material, such as a conductive or insulating material, is polished to planarize the wafer for subsequent process steps.
In a typical CMP process, a wafer is mounted upside down on a carrier in a CMP tool. A force pushes the carrier and the wafer downward toward a polishing pad. The carrier and the wafer typically are rotated above the rotating polishing pad on the CMP tool's polishing table. A polishing composition (also referred to as a polishing slurry) generally is introduced between the rotating wafer and the rotating polishing pad during the polishing process. The polishing composition typically contains one or more chemicals that interact with or dissolve portions of the uppermost wafer layer(s) and one or more abrasive materials that physically remove portions of the layer(s). The wafer and the polishing pad can be rotated in the same direction, in opposite directions, or one of the wafer or polishing pad can be rotated while the other one of the wafer or polishing pad remains stationary. The carrier also can oscillate across the polishing pad on the polishing table. The rotation scheme is chosen according to the particular polishing process being carried out.
It is important in the polishing process to provide sufficient polishing composition between the substrate being polished and the polishing pad. While soft porous polishing pads can act as reservoirs of polishing composition, drawbacks to the use of soft polishing pads have led to the development of harder polishing pads having grooves formed into the surface. The grooves facilitate movement of polishing compositions into the space between the polishing pad and the substrate surface. When the grooves are formed so as to be concentric with the axis of rotation of the polishing pad, in the case of circularly grooved polishing pads, the raised regions of the pad that lie outside of the grooves tend to result in non-uniform polishing of the substrate due to the development of a pattern in the substrate matching the pattern on the polishing pad. This phenomenon has led to the proposal for the use of polishing pads having an “off center” groove pattern, for example, a pad having concentric circular grooves whose center of concentricity does not coincide with the rotational axis of the polishing pad. However, during the formation of the grooves, such as by machining, the groove pattern runs off one side of the polishing pad surface. Because the polishing pad material must necessarily be at least somewhat soft and because many polishing pads are at least somewhat porous, the edge of the polishing pad typically has defects where the grooves meet the edge of the polishing pad that result either from the process used to form the grooves or that form during the polishing process. The edge defects of the polishing pad in turn results in the production of scratching defects in a substrate being polished.
Thus, there remains a need in the art for improved polishing pads.